Magnetron sputtering of various materials onto substrates such as glass panes involves the use of a cathodic target, a magnet to produce a magnetic field adjacent to the target, and an inert gas such as argon which forms a plasma that is contained by the magnetic field. Targets can be of various configurations, but cylindrical targets that rotate about their axes during a sputtering operation are widely used. These targets are usually tubular, and employ a magnet that is positioned within the interior of the target. Although the target rotates about its axis, the magnet commonly does not; rather, the magnet is held in a stationary position as the target rotates.
Unfortunately, it has been found that the targets do not wear uniformly and evenly along their lengths as material is sputtered from the targets' outer surfaces. The erosion that takes place between their end portions similarly is not uniform; although some uniformity of erosion is experienced nearer the center of the target, severe erosion occurs near the target ends.
The result of the uneven erosion pattern is that by the time the target must be replaced due to nearly complete erosion nearer the target ends, the central portion of the target yet retains a substantial amount of sputterable target material. Some improvement in efficiency can be obtained by utilizing dual magnets in which the ends of the magnets are offset from one another. However, better target utilization remains the goal. The replacement of targets from a sputtering apparatus is a considerable job, and of course the sputtering line must be shut down during target replacement.